Offsetting Surfaces

This task explains how to create an offset surface, based on an existing surface.

Open the FreeStyle_Part_39.CATPart document.

  1. Select a surface, or a set of surfaces.
 

  1. Click the Offset icon .
    The offset surface is automatically visualized as a meshed surface.
 

 

  1. Choose the options you wish from the Offset Surface dialog box:
 

  • the offset type: a simple offset creates a surface which points are all at the same distance from the initial surface,
    whereas a variable offset lets you set the offset distance at each corner point of the surface.

  • the limits, that is constraints to be taken into account when computing the offset surface. You can specify whether it should comply with a given tolerance, 
    or it should have a maximum order in U and V. The resulting surface will lie within these constraints.

  • Display, that is the elements to be displayed on the geometry.

You can create an offset by setting the values for the tolerance, u-order and v-order parameters.
To set the step value for the Tolerance, Delta U and Delta V parameters:
  1. Right-click the box and select Change step.
  2. Select the value.
    You can enter a new step value in the New step dialog box by selecting new one.
    1. Right-click the box and select Change step > new one.
      The new step dialog box appears.
    2. In the box, type a new step value.
    3. Click OK.
      These contextual menu option is available in the Tolerance box, Delta U box and Delta V box.

To calculate minimum distance between geometrical entities (Measure Between) and calculate property of any geometrical entity (Measure Item):

  1. Right-click the box and select Measure Between.
    OR
  2. Right-click the box and select Measure Item.
  These contextual menu options are only available in the Tolerance box. 
 

To set the range value for the Tolerance, Delta U and Delta V parameters:

  1. Right-click the box and select Range > Edit.

    The Range definition dialog box appears.
  2. In the Inf. Range box, type a value.
  3. In the Sup. Range box, type a value.
  4. Click OK.
    To add range values perform the following actions: 

       1. Right-click the box and select Range > Suppress.

       2. Right-click Length box and select Add Range….

           The Range definition dialog box appears.
          

 

       3. Select the Inf. Range check box and Sup. Range check box.

        4. Enter the range values and click OK. 
 
The default Range, Step and Value of the Tolerance, U-order and V-order scroll bar in Offset command are as follows:
Scroll Bar Name Range Step Value
Tolerance 0.00001mm to 0.1 mm  0.01 mm  0.02 mm 
U-order  0 to 14  1  2 
V-order  0 to 14   1  2 

When you click the More... button: the type of information to be displayed on the offset surface before it actually is created. This information is useful to let you fine-tune the offset specifications.
 

 
  • Offset values: the distance between any point of the initial surface and the resulting surface.
  • Normals: identifying the direction of the initial surface. Click on the arrow to invert the offset.
  • Order: the order value in U and V
  • Tolerance: the exact tolerance deviation
  • Corners: displays or hides the manipulators at the four corner points (only in Simple mode) to make Snap on Geometry possible. When you are in Variable mode, the Corners option is checked: if you pull the central manipulator, all manipulators are temporarily linked to each other, basically they have the same behavior as regular control points.

  1. By default the Edit dialog box is displayed. If not, right-click the offset value box on the surface to display it, and enter the offset value.
 

  1. Click Close to validate the offset value.

You can also move the pointer over one of the corner points, and directly pull on the displayed manipulators.
The offset value is dynamically modified.

  1. Click OK in the Offset Surface dialog box to create the offset surface.
 

You can also select a point either in the 3D or in the specification tree to impose the offset value.
The value will be set as well as the distance corresponding to the normal projection of the input point onto the surfaces.

 

If no projection is possible, no selection is possible and a message error is issued.
You can also create variable offset:
 

 

  1. Click Variable in the Offset Surface dialog box.

  2. You can modify the delta in order.
    This means that the maximum order number of the offset surface will not exceed the initial surface order number plus the indicated value. Offset values are displayed at each corner of the surface.

  3. Move the pointer over a corner point and drag it in the desired direction to dynamically modify the value.
 

 

  1. Right-click another offset value and using the Edit dialog box, change this value.
    Here we modified two values from 15 to 40.
 

 

  1. Click OK in the Offset Surface dialog box.
    The offset surface is created.
 

  • The same method applies when offsetting a set of surfaces. As all surfaces may not present the same orientation,
    check the Normals option from the Offset Surface dialog box and right-click arrows: a contextual menu displays on each arrow and enables you to Reverse or Adjust all.

  • If the offset is performed on a surface relimited using the break command, the result is a relimited surface,
    even though the pre-visualization presents the initial (not relimited surface):
 

  • If the offset value is superior to the maximum value, an error message is issued. Nevertheless, you can create the offset.
 

Multi-selection of surfaces is available.
Capabilities are available from: